Mechanism of formation of the contractile ring during cytokinesis

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1)rho4 and rho5 genes of fission yeast was cloned. Rho4 regulates localization of F-actin patches and organization of microtubules, and thereby formation of cell wall and the septum. Localization of Rho4 is regulated by RhoGDI while activity of Rho4 is regulated by the RhoGAP Rga92)Sea urchin Cdc42 showed 87% homology to human Cdc42. It binds IQGAP and thus enhancesw actin polymerization. IQGAP localizes to the cleavage furrow during cytokinesis.3)It was established that the C-terminal 134 residues are necessary and sufficient for localization of Myo2 to the division site. This region contains Ser1444 which is phosphorylated during interphase but dephosphorylated during M-phase. This dephosphorylation enables Myo2 to target Mid1 which is transmitted from the nucleus to the equatorial cortex during G2.4)The Rho1GEFs Rgf1 and Rgf2 are localized to the growing ends of fission yeast cell during interphase, while to the septum region during mitosis and are involved in synthesis of cell wall … More and the septum. Rgf3 accumulates at the division site forming a ring during mitosis, and the ring contracts as cytokinesis progresses. Rgf3 is considered to control formation of both the contractile ring and the septum through activation of Rho1.5)We determined directionality of F-actins in the F-actin cables in fission yeast cells by decorating the F-actins using myosin S1. The barbed end of the F-actins in the interphase cables face the growing end of the cell during interphase. During mitosis, it reversed. We proposed a hypothesis that myosin V transports materials necessary for polarized growth of the cell to the cell ends during interphase, while transports those necessary for division to the division site during mitosis.6)Fission yeast actin-depolymerizing factor Adf1 is localized to the F-actin patches during interphase and to the contractile ring during mitosis and cytokinesis. Adf1 is involved in formation of the contractile ring through its F-actin-severing activity. Its binding to F-actin in the cell is competitive with the tropomyosin Cdc8. It was also found that Adf1 cooperates with myosin-II in formation of the contractile ring. We propose that Adf1 is necessary for formation and stability of the contractile ring. Less